www.geologicacarpathica.sk
GEOLOGICA CARPATHICA, OCTOBER 2009, 60, 5, 345—350 doi: 10.2478/v10096-009-0026-z
SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the
Malé Karpaty Mountains (Western Carpathians): evidence of
Meso-Hercynian successive S- to I-type granitic magmatism
MILAN KOHÚT
1
, PAVEL UHER
2
, MARIÁN PUTIŠ
3
, MARTIN ONDREJKA
3
,
SERGEY SERGEEV
4
, ALEXANDER LARIONOV
4
and ILYA PADERIN
4
1
Dionýz Štúr State Institute of Geology, Mlynská dolina 1, 817 04 Bratislava, Slovak Republic; milan.kohut@geology.sk
2
Department of Mineral Deposits, Faculty of Natural Sciences, Comenius University, Mlynská dolina G, 842 15 Bratislava,
Slovak Republic
3
Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University, Mlynská dolina G, 842 15 Bratislava,
Slovak Republic
4
All-Russian Geological Research Institute (VSEGEI), Sredny Prospekt 74, 199106 St.-Petersburg, Russia
(Manuscript received February 26, 2009; accepted in revised form June 25, 2009)
Abstract: Representative granitic rock samples from the Malé Karpaty Mountains of the Western Carpathians (Slovakia)
were dated by the SHRIMP U-Th-Pb isotope method on zircons. Oscillatory zoned zircons revealed concordant Missis-
sippian magmatic ages: 355 ± 5 Ma in Bratislava granodiorite, and 347 ± 4 Ma in Modra tonalite. The results document
nearly synchronous, successive Meso-Hercynian plutonic events from S-type to I-type granites. The Neo-Proterozoic
inherited zircon cores (590 ± 13 Ma) were identified in the Bratislava S-type granitic rocks whereas scarce Paleo-Protero-
zoic inherited zircons (1984 ± 36 Ma) were detected within the Modra I-type tonalites.
Key words: Western Carpathians, Malé Karpaty Mts, Bratislava Massif, Modra Massif, granitic rocks, zircon, SHRIMP dating.
Introduction
A typical feature of the Hercynian orogeny in Europe is pro-
duction of voluminous felsic igneous rocks during the subduc-
tion-collisional processes. The granitic rocks form an
important constituent of the Western Carpathians basement
(WCB). Geodynamic evolution of the WCB is comparable to
the other Hercynides of Western and Central Europe, such as
the Iberian Massif, Massif Central, Bohemian Massif. Peralu-
minous S-type, calk-alkaline I-type, post-orogenic subalkaline
A-type and ore specialized S
s
-type of granitic rocks were iden-
tified in the Western Carpathians (see review of Petrík et al.
2001). However, Carboniferous S-type granodiorites – gran-
ites and I-type tonalites – granodiorites dominate in the
WCB at the present erosion level and their distribution is asso-
ciated with distinct thermal and tectonic events. Available iso-
topic datings (Rb-Sr WR isochrons, conventional U-Pb zircon
data) suggest a time gap (30—40 Ma) in the genesis of the two
types of granitic rocks (Petrík et al. 2001). However, there is
still a general lack of modern isotope data within the WCB.
The aim of our study is to present the new age relationship
and discuss the evolution of both S- and I-type granitic rocks
from the Malé Karpaty Mts using the SHRIMP U-Th-Pb dat-
ing on zircon.
Geological setting
The Malé Karpaty Mountains represent a typical core
mountain of the Tatric Unit situated in Western Slovakia, a
SW part of the Central Western Carpathians. The Bratislava
and the Modra granitic massifs are dominant parts of the
Malé Karpaty Mts forming their pre-Alpine basement be-
tween Bratislava and Modra towns (Fig. 1), and in the Hunds-
heimer Berge on the right side of the Danube river near
Hainburg town, NE Austria.
The granitic rocks of the Malé Karpaty Mountains consist
of a Hercynian orogeny related plutonic peraluminous gra-
nitic suite with S-type (Bratislava Massif) and calc-alkaline
I-type (Modra Massif) geochemical affinity (e.g. Cambel &
Vilinovič 1987; Petrík et al. 2001). They exhibit a distinct
intrusive and thermal metamorphic contact with adjacent
Lower Paleozoic (Silurian to Devonian) metapelites to
metapsammites and amphibolitic metabasic rocks (Kori-
kovsky et al. 1984; Korikovsky in Krist et al. 1992). The
dominant rocks of the Bratislava Massif are biotite to musco-
vite-biotite granodiorites, monzogranites to leucocratic syeno-
granites and widespread pegmatite-aplite dikes, whereas
biotite (leuco)tonalites and granodiorites and subordinate to
lacking granites and pegmatites are typical features of the
Modra Massif (Cambel & Vilinovič 1987; Petrík et al.
2001). Small bodies of biotite-amphibole diorites occur in
both massifs. The first K-Ar isotopic geochronological data
for K-feldspar and micas from the Bratislava Massif indicat-
ed mainly Upper Paleozoic, Carboniferous to Permian ages
(348 ~ 281 Ma, Kantor 1959; Bagdasaryan et al. 1977), which
were later also confirmed by the whole-rock Rb-Sr isochrone
age (347 ± 4 Ma, Bagdasaryan et al. 1982), and Th-U-Pb elec-
tron-microprobe monazite dating (355 ± 18 Ma, Finger et al.
2003; 353 ± 2 Ma, Uher et al. submitted). Geochronological
346
KOHÚT, UHER, PUTIŠ, ONDREJKA, SERGEEV, LARIONOV and PADERIN
data from the Modra Massif revealed slightly younger Her-
cynian ages: 326 ± 22 Ma by the whole-rock Rb-Sr isochron
method (Bagdasaryan et al. 1982), ~ 320 Ma by the zircon
U-Pb dating (Scherbak et al. 1988), and 345 ± 22 Ma by the
Th-U-Pb electron-microprobe dating of monazite (Finger et al.
2003), respectively 355 ± 18 Ma from identical sample MK-72
(Kohút, unpublished data). However, some K-Ar data from
both the Bratislava and Modra Massifs also gave younger, Pa-
leo-Alpine Jurassic to Cretaceous ages (190 to ~ 80 Ma, Bag-
dasaryan et al. 1977; Bagdasaryan in Cambel et al. 1990).
Sampling and methods
For the SHRIMP dating, the following samples were se-
lected:
MK-66: medium-grained, slightly porphyric biotite grano-
diorite.
Bratislava-Devín,
large
operating
quarry,
[48
°09’47.54” N; 17°00’17.81” E, alt. 226 m]. This sample
consists of 34.4 vol. % of quartz, 37.8 vol. % of plagioclase,
18.5 vol. % of K-feldspar, 8.1 vol. % of biotite, 0.3 vol. % of
muscovite, and 1.0 vol. % of accessories (zircon, apatite,
monazite, ilmenite); Eltinor point count = 2173.
MK-72: medium-grained biotite tonalite. Modra-Piesok,
natural outcrops in the Krištofka area, [48
°23’45.12” N;
17
°14’37.06” E, alt. 548 m]. Mineral content is: 32.6 vol. %
of quartz, 49.1 vol. % of plagioclase, 5.2 vol. % of K-feldspar,
11.4 vol. % of biotite, and 1.7 vol. % of accessories (apatite,
zircon, allanite, epidote, monazite, magnetite); Eltinor point
count = 2254.
The heavy-mineral separation of accessory zircon was per-
formed at the Comenius University and Geological Institute,
Slovak Academy of Sciences in Bratislava, using a common
separation procedure (crushing, sieving, gravitation separa-
tion by using Wilfley table, heavy liquid – bromophorm,
and electro-magnetic separation). Euhedral transparent crys-
tals of zircon, usually 150 to 450 µm in size, were selected for
dating. The zircon sample preparation and the SHRIMP dating
were done at the All-Russian Geological Research Institute
(VSEGEI) in St.-Petersburg; the procedure includes BSE, CL
(using CamScan MX 2500S with detector CLI/QUA 2) and
optical imaging of the polished mounts with zircon crystals
for the choice of the measured spots. The age measurements
were performed using the SHRIMP II apparatus, the high-
resolution five-collector secondary ion mass-spectrometer
(ion microprobe) of ASI (Australian Scientific Instruments)
zircon TEMORA was used as the standard (Black et al.
2003). The ion beam on the dating area was 25 µm in diame-
ter. Nearly all the measured spots provided concordant ages,
which fall on calculated concordia curves. Reproducibility
of concordant zircon U-Pb analyses (10 measurements) is
1.5 % or better. Error in standard calibration was 0.54 %. In
both measured samples, 10 spots from 5 or 6 different zircon
crystals have been measured per rock sample. Detailed me-
thodics concerning measurement and age calculations can be
found in the works of Larionov et al. (2004) and/or Putiš et
al. (2008). The measured isotope data are summarized in
Tables 1 and 2.
Results
The SHRIMP dating reveals three distinct concordant to near-
ly concordant age populations in the Bratislava Massif: (1) Neo-
Proterozoic to Cambrian, (2) Mississippian Meso-Hercynian,
and (3) Jurassic Paleo-Alpine (Table 1, Fig. 2A—B).
Fig. 1. Position of the studied granitic rocks in the Bratislava and
Modra Massifs of the Malé Karpaty Mts [simplified geological
sketch modified from Cambel & Vilinovič (1987)]. Explanations:
1 – Lower Paleozoic metasedimentary rocks en bloc, 2 – metaba-
sic rocks, 3 – diorites, 4 – granitic rocks of the Bratislava Massif,
5 – granitic rocks of the Modra Massif, 6 – Mesozoic rocks en
bloc, 7 – Cenozoic sedimentary rocks en bloc, 8 – settlement.
348
KOHÚT, UHER, PUTIŠ, ONDREJKA, SERGEEV, LARIONOV and PADERIN
Bratislava Massif
Zircons of the oldest (1) population show apparent regular
oscillatory zoning crystals or cores; they give Neo-Protero-
zoic ages of 591 ± 8, 588 ± 10 and 534 ± 7 Ma (Table 1,
Fig. 3A). The Meso-Hercynian zircon population (2) is dom-
inant; the zircons form cores or long prismatic crystals with
fine oscillatory zoning (Fig. 3A). They yield a relatively nar-
row age interval of 359 ± 5 to 350 ± 7 Ma (5 spots; Table 1,
Fig. 2B). The two Paleo-Alpine ages (177 ± 2 and 183 ± 3 Ma)
of population (3) were obtained from oscillatory zoned zir-
con overgrowths on probably older crystals with different
crystal morphology, U and common Pb concentrations and
low CL signal (Table 1, Figs. 2A, 3A).
Modra Massif
Zircons from the Modra Massif show two age populations:
(1) Paleo-Proterozoic and (2) Mississippian Meso-Hercynian
(Table 2, Fig. 2C—D).
Two spot datings from a large oval shaped inherited zircon
with irregular zoning revealed ages between 1802 ± 24 and
2029 ± 25 Ma (Fig. 3B). However, their projections are dis-
cordant with an upper intercept of 1984 ± 36 Ma and 0 Ma at
a lower intercept (Fig. 2C).
Short prismatic zircon with distinct oscillatory zoning
show Hercynian ages, six of them exhibit a narrow interval
between 340 ± 5 and 350 ± 5 Ma, with an average nearly con-
cordant age of 347 ± 4 Ma (Table 2, Figs. 2D, 3B).
Discussion and conclusion
The SHRIMP U-Th-Pb dating of zircon represents
a sensitive isotopic method with a large advantage for the
dating of zircons from orogen-related S- and I-type granitic
rocks with a complex crystallization history. The Bratislava
and Modra Massifs are typical examples of the West-Car-
pathian Hercynian intrusive suites incorporated in the
younger Alpine terranes. Zircons from both massifs revealed
the presence of older inherited Paleo-Proterozoic (Modra)
cores or Neo-Proterozoic to Cambrian (Bratislava) cores.
Similarly, old Precambrian (Archean to Proterozoic) ages
have been reported from several Paleozoic (meta)granitic
suites of the Western Carpathians (Cambel et al. 1990; Poller
et al. 2001; Putiš et al. 2008). However, most data from zir-
cons indicate Meso-Hercynian, Mississippian ages for both
massifs: 355 ± 5 Ma and 347 ± 4 Ma, for Bratislava and Modra,
respectively. The results obtained are in accordance with older
whole-rock Rb-Sr and electron-microprobe Th-U-Pb mona-
zite datings of the Bratislava Massif (Bagdasaryan et al.
1982; Finger et al. 2003; Uher et al. submitted). However,
our new data for the Modra Massif ruled out the possibility
Fig. 2. U-Pb isotope concordia diagrams of the Malé Karpaty Mts gra-
nitic rocks: A – Bratislava Massif – all measurements; B – Bratisla-
va Massif – the Hercynian population; C – Modra Massif – all
measurements; D – Modra Massif – the Hercynian population.
350
KOHÚT, UHER, PUTIŠ, ONDREJKA, SERGEEV, LARIONOV and PADERIN
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